We found way to track those necromancers.

Adventurers met with employer inside "Social Unicorn" bar. Then they found the magician named Anna who agreed to help them find necromancers in exchange of finding her dog that ran away inside dangerous tomb. They followed dog's footprints and after some time found dog playing with big stone golem inside big room. Golem attacked them but they were able to destroy him. They returned to Anna and got the info about necromancer's whereabouts.